A certification could definitely be useful if you are looking for a Java developer position, but it's certainly not a guarantee. But it might make the difference between some equivalent candidates. It shows different positive aspects for a programmer: eager to learn, want to study and improve your knowledge (in your own time), you are up for a challenge, you have an eye for details,... But you probably not get a job just because you are certified. So a certification is never a guarantee for a job, but it may help turn the scale in your favor. In this thread and this one you'll find some advice to increase your chances to get an entry-level job as a Java developer.